ASTM C1256-93(1998)e1
(Practice)Standard Practice for Interpreting Glass Fracture Surface Features
Standard Practice for Interpreting Glass Fracture Surface Features
SCOPE
1.1 Fracture features on the surface of a crack reflect the nature and course of the fracture event associated with the breakage of a glass object. This practice is a guide to the identification and interpretation of these fracture surface features.
1.2 The practice describes the various fracture surface features as to their appearance, the process of formation and their significance.
1.3 The practice does not provide the procedural information necessary for a complete fractographic analysis. Such information is available in the general literature. (See Glossary for suggested literature).
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Designation: C 1256 – 93 (Reapproved 1998)
Standard Practice for
Interpreting Glass Fracture Surface Features
This standard is issued under the fixed designation C 1256; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Editorial changes were made in Sections 3 and 6 in February 1999.
1. Scope determining the origin and the nature of the local stresses that
produced the fracture.
1.1 Fracture features on the surface of a crack reflect the
3.1.7 fracture system—the fracture surfaces that have a
nature and course of the fracture event associated with the
common cause or origin.
breakage of a glass object. This practice is a guide to the
3.1.8 terminal velocity—the uppermost limiting velocity at
identification and interpretation of these fracture surface fea-
which a crack can propagate in a material, the approach to
tures.
which is marked on the fracture generated surface by the
1.2 The practice describes the various fracture surface
presence of mist. The terminal velocity is approximately one
features as to their appearance, the process of formation and
half the velocity of sound in the material.
their significance.
3.1.9 uniform stress—a state of stress that does not change
1.3 The practice does not provide the procedural informa-
within the region of concern.
tion necessary for a complete fractographic analysis. Such
information is available in the general literature. (See Glossary
4. Summary
for suggested literature).
4.1 This practice is intended to aid in the identification of
2. Referenced Documents fracture surface markings as well as to assist in the understand-
ing of their formation and significance.
2.1 ASTM Standards:
C 162 Standard Terminology of Glass and Glass Products
5. Significance and Use
3. Terminology 5.1 Fractography is often used to help identify the events
that have resulted in the fracture of a glass object. This practice
3.1 Definitions:
defines the appearance of various fracture surface features, as
3.1.1 bending stress—a continuously and linearly changing
well as their method of formation. Thus, there can be a
stress across the thickness of a glass body, varying from
common understanding of their relationship to the fracture
compression on one surface to tension on the opposite surface.
process as well as a common terminology.
3.1.2 forking—a mechanism whereby a propagating frac-
ture branches into two fractures, separated from each other by
6. Fracture Surface Markings
an acute angle.
6.1 Origin:
3.1.3 forking angle—the angle subtended by two immedi-
6.1.1 Identification—The origin is almost always found at
ately adjacent fractures which have just branched or forked.
the junction where the fracture-generated surface meets a free
3.1.4 fracture mirror constant—a constant, characteristic of
surface or a dissimilar material. Commonly, the origin is
a given glass composition, which, when divided by the square
symmetrically located near the apex of the mirror and it is
root of the fracture mirror radius, will yield the fracture stress.
usually small compared to the mirror. Fig. 1 shows typical
3.1.5 fracture mirror radius—a dimension of the fracture
origins and mirrors bounded by mist.
mirror as measured along the original specimen surface. It is
6.1.2 Formation—The origin represents the single, unique
defined as the distance from the origin to the first detectable
location at which every fracture system begins to form.
mist.
6.1.3 Significance—The origin defines the location where
3.1.6 fracture surface markings—features of the fracture
the fracture began. It may contain the stress concentrator or it
surface produced during the fracture event which are useful in
may be the stress concentrator.
6.2 Mist Region:
This practice is under the jurisdiction of ASTM Committee C-14 Glass and
6.2.1 Identification—Under low power (5 − 50 3 ) magni-
Glass Products and is the direct responsibility of Subcommittee C14.04 on Physical
fication, it has a misty appearance. Proceeding away from the
and Mechanical Properties.
origin, it becomes more fibrous in appearance and elongated in
Current edition approved Dec. 15, 1993. Published February 1994.
the direction of crack spread. (See Fig. 2.)
Annual Book of ASTM Standards, Vol 15.02.
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C 1256 – 93 (1998)
6.3.3 Significance—It is often helpful in locating the origin.
The shape defined by the mist boundary is indicative of the
uniformity of the stress field at the time of failure, for example;
an open mirror, defined by mist only along the original surface,
implies bending; a semicircular mirror implies uniform ten-
sion: (See Fig. 1) The mirror dimensions may be used to
calculate the stress at breakage, because the mirror radius is
inversely proportional to the square of the stress at the time the
mirror was formed. If the mirror is symmetrical, then use the
radius to the mist boundary. To calculate the stress at breakage
when the mirror is not symmetrical, the mirror radius is best
determined by dividing the mirror diameter by two. A more
detailed description of the relationship between the mirror and
the breaking strength for various glasses is found on p. 364 of
(1) and in (2) and (3). Further discussion on quantitative
fracture analysis techniques is well summarized in (4).
6.4 Wallner Lines:
FIG. 1 Origin Areas Produced Under Various Stress Functions
6.4.1 Identification—Wallner lines, also called ripple marks,
and Their Typical Fracture Features
are rib-shaped marks, frequently appearing as a series of
curved lines resembling ripples created when an object is
dropped into still water. (See Figs. 3-8.)
6.4.2 Formation—They are produced when the plane of the
propagating crack front is temporarily altered by an elastic
pulse.
6.4.3 Significance—The direction of local propagation is
perpendicular to the Wallner lines; it proceeds from the
concave to the convex side of the line. The shape of the line
indicates the direction of stresses at various points on the crack
front. The more advanced portions of the line generally
correspond to regions of higher tension.
6.5 Wallner Lines, Primary:
6.5.1 Identification—Primary Wallner lines are usually
quite distinct and always have their source associated with
some discontinuity which was present before fracture. Ex-
amples would include bubbles or other inclusions, surface
damage or an abrupt change in surface contour. (See Fig. 3 and
Fig. 4.)
6.5.2 Formation—They result from the interaction of a
propagating crack with an elastic pulse coming from the
FIG. 2 An Origin Area, with Mirror and Mist
encounter of the crack front with a preexisting discontinuity.
6.5.3 Significance—The convex side is toward the direction
6.2.2 Formation—It is produced as the crack front breaks
of crack propagation. Primary Wallner lines can be used to
into numerous segments, which then round into one another.
Their propagation aborts as the crack front approaches terminal
velocity.
6.2.3 Significance—It defines the limit of the mirror region
and indicates that the crack has nearly reached terminal
velocity, or both.
6.3 Mirror:
6.3.1 Identification—The mirror is a smooth portion of the
fracture surface surrounding the origin (see Fig. 2). It is
commonly bounded by mist, but mist may not form when the
local stress at the fracture front diminishes as the crack
extends.
6.3.2 Formation—It represents the initial portion of the
propagating crack where the velocity is accelerating from the
origin to a value sufficient to induce turbulence at the crack
front, that is, approaching terminal velocity, where mist and
FIG. 3 Primary Wallner Lines Generated From a Surface
forking may appear. Nonconformity and an Inclusion
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C 1256 – 93 (1998)
FIG. 4 Primary Wallner Lines Generated; (a) From Surface
Scratches, (b) A Bubble Generating Gull Wings
FIG. 5 Secondary Wallner Lines Generated From Mist Formation
determine whether a discontinuity was present before or after
the breakage occured. In thin glassware, the crack breaking
through to the opposite surface will generate a primary Wallner
line which indicates the stress distribution at the time of failure.
FIG. 6 Secondary Wallner Lines Generated From Mist Formation
6.6 Wallner Lines, Secondary:
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C 1256 – 93 (1998)
6.7.3 Significance—They indicate that the failure resulted
from a mechanical shock, where an elastic pulse was generated
outside the plane of crack propagation.
6.8 Dwell Mark:
6.8.1 Identification—Dwell marks, also called arrest lines,
have a similar rib-shaped contour to that of Wallner lines but
are distinctly sharper, often exhibiting a noticeable change in
fracture plane after the mark and may have twist hackle
associated. (See Fig. 9 and Fig. 10.)
6.8.2 Formation—They are formed when there is an abrupt
change in the direction of the stress field such as when the
crack stops and then is restarted by a different stress field.
6.8.3 Significance—They indicate that the crack stopped
propagation along a given plane and was restarted by a
FIG. 7 Tertiary Wallner Lin
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